1. Field of the Invention
The present invention relates to a semiconductor device having a barrier metal layer made of a refractory metal film and a method for manufacturing the same and, more particularly to, the semiconductor device having the barrier metal layer with a barrier property which is improved by inhibiting crystallization of the barrier metal layer and the method for manufacturing the same.
2. Description of the Related Art
With the increasing integration density of Large Scale Integrations (LSIs), contact holes need to be more and more finely patterned, thus increasing an aspect ratio, i.e. a value of a depth of the contact hole divided by its diameter. With this, a layer made of aluminum or other metal formed by a conventional sputtering method, which has rather poor step coverage, may cause an increase in contact resistance at a contact hole or, possibly, disconnection at it. Even if wiring is possible, moreover, there might occur such an electro-migration phenomenon that a current flow would cause migration of aluminum atoms, so that the wiring is liable to be disconnected, thus problematically lowering a reliability.
To solve this problem, such a method has been employed that metal having good step coverage is buried in the contact hole.
A typical one of such methods is a tungsten-plug method whereby a tungsten layer excellent in step coverage formed by a Chemical Vapor Deposition (CVD) method is buried in the contact hole. According to this tungsten-plug method, first a titanium film is formed in the contact hole by a sputtering method to reduce connection resistance (contact resistance) of the contact hole, then, a barrier metal film made of titanium nitride is formed in the contact hole by the sputtering method to enhance adherence between this titanium film and the tungsten layer as well as to prevent the tungsten layer from penetrating into a substrate, and then the tungsten layer is buried into the contact hole by the CVD method, and then the tungsten layer is etched back overall to be left only in the contact hole, thus forming a tungsten plug. With this method also, as the fine patterning of the contact hole advances and therefore its aspect ratio is increased, the sputtering method becomes unable to form the titanium film or titanium nitride film, i.e. barrier metal layer, to a desired thickness in the contact hole. This may lead to increase in contact resistance or destruction of circuit elements by the tungsten layer.
To guard against this, it has been attempted to form the titanium film and the titanium nitride film by the CVD method. This thermal-reaction CVD method is widely used because the titanium film nitride formed by such CVD method as utilizing thermal reaction is most excellent in step coverage. Note here that the contact hole is filled with the titanium film, the titanium nitride film, and a tungsten film, all three of which are formed by the CVD method.
First, as shown in FIG. 3A, on a silicon substrate 301 on which element-isolating regions are defined by field insulator films (not shown), a silicon oxide film 302 is formed as an inter-layer insulator film to a thickness of 1.5 xcexcm by the CVD method.
Next, as shown in FIG. 3B, a photo-resist film 303 is formed on the silicon oxide film 302 and then patterned by typical photolithography so as to make an opening at positions where a contact hole 304 is to be formed. Using this photo-resist film 303 as a mask, dry etching is performed to form the contact hole 304 in this silicon film 302 which reaches the silicon substrate 301. This contact hole 304 has a diameter of approximately 0.4 xcexcm.
Next, as shown in FIG. 3C, the photo-resist film 303 is removed and then a titanium film 305 is formed. Specifically, this titanium film 305 is formed to a thickness of 10 nm by the CVD method, whereby a plasma is generated by flowing a gas mixture containing 10 sccm (standard cubic centimeter per minute) of titanium tetra-chloride and 1000 sccm of argon (Ar), setting an intra-chamber pressure at 20 Torr and a wafer temperature at 500xc2x0 C. or higher, and applying several hundreds of watts of high-frequency power between the opposing electrodes of the silicon substrate 301.
Next, as shown in FIG. 3D, a first titanium nitride film 306 is formed on the titanium film 305 to a thickness of 60 nm. Specifically, this first titanium nitride film 306 can be formed by flowing 50 sccm of titanium tetra-chloride, 100 sccm of ammonia, and 50 sccm of nitrogen, setting the intra-chamber pressure at 30 Torr, and heating a susceptor so that the wafer temperature would be 600xc2x0 C.
Next, as shown in FIG. 3E, a tungsten film 307 is formed overall by the CVD method to fill the contact hole 304. In fact, the tungsten film 307 is formed in two steps of nucleation and hole filling. Specifically, after the semiconductor substrate 301 is heated to 450xc2x0 C., a gas mixture is introduced which contains 10 sccm of mono-silane, 20 sccm of tungsten hexa-fluoride, 800 sccm of argon, and 1000 sccm of hydrogen and setting the intra-chamber pressure at 30 Torr by use of a pressure regulating valve to perform the tungsten film 307 formation for about 10 seconds.
After nucleation is thus performed on the silicon substrate 301, continuously a gas mixture is introduced which contains 95 sccm of tungsten hexa-fluoride, 600 sccm of argon, and 1000 sccm of hydrogen and setting the intra-chamber pressure at 90 Torr to perform the tungsten film 307 formation for about 50 seconds in order to fill the contact hole 304. Under these conditions, the tungsten film 307 is formed to a thickness of about 5000 xc3x85 on the silicon oxide film 302.
Next, as shown in FIG. 3F, part of the tungsten film 307 in the contact hole 304 being left as is, the other part of the tungsten film is etched back and removed by use of a gas containing sulfur hexa-fluoride, to expose the surface of the first titanium nitride film 306.
Next, as shown in FIG. 3G, an aluminum-alloy film 308 is deposited overall by the sputtering method and patterned into a desired wiring by photolithographic and dry etching methods, to complete an aluminum wiring.
According to the above-mentioned prior-art technologies, however, the first titanium nitride film 306 formed by the thermal CVD method is of a prismatic polycrystalline construction and so has a lot of grain boundaries with insufficient barrier nature. To improve the barrier property, it is effective to increase the thickness of the first titanium nitride film 306, which may destroy a diffused layer formed in the silicon substrate 301 surface and also may result in increase in the aspect ratio of the contact hole 304 into which tungsten plug 309 is to be buried. When the titanium nitride film 306 is formed by the CVD method, in particular, the titanium nitride film 306 titanium nitride film 306 is subject to larger stress, which may cause cracking in the first titanium nitride film 306 or its flaking-off, thus reducing manufacturing yield.
In view of the above, it is an object of the present invention to provide a semiconductor device having a barrier metal layer which can improve a barrier property and prevent lowering of manufacturing yield without destruction of diffused layers in a substrate surface nor deterioration of an aspect ratio of contact holes and a method for manufacturing a same.
According to a first aspect of the present invention, there is provided a semiconductor device having a barrier metal layer, including:
a semiconductor substrate;
an insulator film having a through hole therein formed on the semiconductor substrate;
a first refractory metal nitride film which is formed on an inside surface of the through hole in the insulator film and a surface of which is oxidized or in a surface of which oxygen is absorbed; and
a second refractory metal nitride film which is formed on the first refractory metal nitride film and which has taken in oxygen.
In the foregoing, the preferable mode is one that wherein further includes a metal region buried in the through hole.
Also, according to a second aspect of the present invention, there is provided a semiconductor device having a barrier metal layer, including:
a semiconductor substrate;
an insulator film which is formed on the semiconductor substrate and which has a trench therein;
a first refractory metal nitride film which is formed on an inside surface of the trench in the insulator film and a surface of which is oxidized or into a surface of which oxygen is absorbed; and
a second refractory metal nitride film which is formed on the first refractory metal nitride and which has taken in oxygen.
In the foregoing, the preferable mode is one that wherein further includes a metal region buried in the trench.
Also, the preferable mode is one that wherein further includes:
a third refractory metal nitride film which is formed on the insulator film and the metal region buried in the trench and a surface of which is oxidized or into a surface of which oxygen is absorbed;
a fourth refractory metal nitride film which is formed on the third refractory metal nitride film and has taken in oxygen; and
an insulator film which is formed on the fourth refractory metal nitride film and which has an insulator film having a through hole therein at a position aligned with the metal region.
Also, according to a third aspect of the present invention, there is provided a method for manufacturing a semiconductor device having a barrier metal layer, including the steps of:
forming an insulator film on semiconductor substrate on which elements are formed;
selectively removing the insulator film at a predetermined region, to form a through hole at which a underlying conductive layer is exposed;
depositing a metal film;
depositing a first refractory metal film on the metal film;
oxidizing a surface of the first refractory metal nitride film or absorbing oxygen into the surface; and
depositing a second refractory metal nitride film on the first refractory metal nitride film.
In the above third aspect, a preferable mode is one wherein the metal film is a refractory metal film, refractory metal alloy film, a refractory metal silicide film, refractory metal nitride film, low-resistance metal film or a like.
Also, the preferable mode is one wherein the first and the second refractory metal nitride films are titanium nitride films formed by a Chemical Vapor Deposition method (CVD).
Also, the preferable mode is one wherein the step of oxidizing a surface of the first refractory metal nitride film or absorbing oxygen into the surface is an oxygen-plasma irradiation method.
Furthermore, according to a fourth aspect of the present invention, there is provided a method for manufacturing a semiconductor device having a barrier metal layer, including the steps of:
forming an insulator film on a semiconductor substrate; selectively removing the insulator film at a predetermined position, to form a trench;
a depositing a first refractory metal film;
oxidizing a surface of the first refractory metal nitride film or absorbing oxygen into the surface; and
depositing a second refractory metal nitride film on the first refractory metal nitride film.
In the above fourth aspect, the preferable mode is one that wherein further includes the steps of:
forming a metal film on the second refractory metal nitride film;
with only parts of the first and the second refractory metal nitride films and the metal film formed in the trench being left as are, removing other parts on the insulator film;
forming a third refractory metal nitride film a surface of which is oxidized overall or into a surface of which oxygen is absorbed;
forming a fourth refractory metal nitride film on the third refractory metal nitride film; and
forming an insulator film having a through hole at a position which is aligned with the metal region, in the fourth refractory metal nitride film.
Also, the preferable mode is one wherein the first and the second refractory metal nitride films are titanium nitride films formed by a Chemical Vapor Deposition method.
Also, the preferable mode is one wherein the step of oxidizing a surface of the first refractory metal nitride film or absorbing oxygen into the surface is an oxygen-plasma irradiation method.
With the above configurations, after a titanium nitride film is formed, its surface is oxidized or oxygen is absorbed into it, then on it another titanium nitride film is formed. With this, the second titanium nitride film thus formed on the oxidized surface of the first titanium nitride film grows as taking in oxygen, so that its crystallization is inhibited, resulting in a remarkably small number of grain boundaries left. Thus, by the present invention, the titanium nitride film grows as taking in oxygen, hence in an amorphous manner, with a very small number of grain boundaries left. Therefore, atoms are inhibited from migrating through the grain boundaries, thereby improving the barrier property. Therefore, the barrier layer can be made thinner.